1. Field of the Invention
The present invention relates, generally, to methods and apparatus for manipulating charged particles, for example, electrons or ions, particularly, for controlling the flow of charged particles, for example, for blanking, in lithographic fabrication methods.
2. Description of Related Art
Electron Beam Lithography (EBL) is one of the most important and most widely used methods for nano-fabrication. The primary advantage of electron beam lithography is its high resolution, and its ability to expose nanometer features without a mask. EBL is also the preferred technique for mask manufacturing supporting the integrated circuit industry. On the other hand, one of the key limitations of electron beam lithography is throughput, that is, it takes a relatively long time to expose dense patterns. Slow blanking speed is one of the major bottlenecks for the system speed.
EBL is used principally in three applications in the semiconductor industry. The first is in mask making, typically the chrome-on-glass masks used by optical lithography tools are fabricated by EBL. The second application is direct write for advanced prototyping of integrated circuits and manufacture of small volume specialty products. Finally, EBL is used for research into the scaling limits of integrated circuits and studies of quantum effects and other novel physical phenomena at very small dimensions. Aspects of the present invention may be employed in any one or all of these applications.
An electron beam lithography system is usually a complicated system consisting of numerous software and hardware components. The hardware components include the electron beam column, high voltage power supply, high vacuum system, stage, and electronic control system. The software components include the pattern design, storage and generation software, and proximity effect correction software. The part of electron beam lithography system that forms the electron beam and performs lithography is often referred to as “the column.” A column typically consists of an electron source, two or more lenses, a mechanism for deflecting the beam, a “blanker” for turning the beam on and off, a “stigmator” for correcting any astigmatism in the beam, apertures for helping to define the beam, an alignment systems for centering the beam in the column, and finally, an electron detector for assisting with focusing and locating marks on the sample.
The blanker and deflectors are typically the critical components in electron lithography system, and they are essential to provide the “maskless” patterning ability that characterizes EBL.
In the conventional art, blanking, or turning the electron or charged particle beam on and off, is usually accomplished with an electric field between a single pair of parallel plates set up as a simple electrostatic deflector. Blanking voltages on the plates are provided from electronic drivers to the deflector plates. When the beam is in use, the blanking voltage is static at substantially zero volts, and the beam is typically uninterrupted. When the beam is not needed, static “blanking voltages” are applied on the deflector plates. The charged particles, for example, electrons, in the beam are deflected off beam axis by the electrostatic field between the deflector plates. Typically, the beams can be blocked by an aperture edge or “knife-edge” that is designed to stop the beam. Double-deflection blanking is an improvement of the basic single parallel plate pair design. Similar to the single-deflection blanker, an electrostatic field is used to deflect the beam to a beam stop using two sets of plate electrodes.
One of the key limitations of EBL is its relatively low throughput. Compared to optical lithography, the throughput of EBL could be one or more magnitude lower. There are several factors contributing to the total time needed for a lithography job, including exposure time (determined by the area needed for exposure, resist sensitivity, and beam current) shape-to-shape overhead (including the settling time for blanker and deflectors) stage movement overhead (determined by the mechanical design of the stage, the weight of stage and wafer, etc.) wafer-to-wafer overhead (including the pumping time and preparation time for wafers). The exposure time is the most essential part of the EBL operation. However, various overheads can also be significant in some cases.
Improved blanker design can have a positive impact on system throughput. First, an improved blanker design can reduce blanker settling time, which is a direct contribution to shape-to-shape overhead; and, second, an improved blanker can provide support for the fast scanning speed enabled by sensitive resist or high beam current.
Aspects of the present invention provide improved blankers, methods, devices, and systems for blanking, especially, blanking in photolithographic applications. Moreover, it is recognized that aspects of the present invention are not limited to use with EBL or lithography, but may be applied to any application where the manipulation of charged particles is advantageous.